Mesoporous silica, mesoporous silica composite material, and processes for production thereof

ABSTRACT

A mesoporous silica is provided, having uniform mesopores and a periodic structure, which contains Zr in the form of a Si—O—Zr bond. The Zr content in the Si—O—Zr bond, represented by [Zr/(Si+Zr)], is 0.05 to 20 mole %. The mesoporous silica is superior in alkaline resistance and is suitably used as a separation membrane (e.g. a ceramic membrane) and a catalytic support for a solid-liquid system, in which an alkaline liquid may be used.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a mesoporous silica, a mesoporoussilica composite material, and processes for producing such a silica andsuch a composite material. More particularly, the present inventionrelates to a mesoporous silica and a mesoporous silica compositematerial, both having superior alkaline resistance and being suitablyused particularly as a separation membrane (e.g. a ceramic membrane) ora catalytic support for solid-liquid system, in which an alkaline liquidmay be used; as well as to processes for producing such a silica andsuch a composite material.

In recent years, attention has been paid to mesoporous silica with auniform mesopore structure, typified by MCM-41 (see JP-A-5-503499) andFSM-16 (see J. Am. Chem. Soc., 114, 10834, 1992). Mesoporous silica issynthesized using the micelle structure of a surfactant as a template;therefore, mesoporous silica has a structure in which pores with nanometer size in diameter are arranged periodically, and the size of thepore diameter is dependent upon the carbon chain length of thesurfactant. Accordingly, mesoporous silica is characterized in that ithas pores with uniform diameter and the diameter can be controlledappropriately. Owing to these characteristics, mesoporous silica isexpected to be used as a separation membrane enabling a high selectivityand a catalytic support with high performance; and processes forsynthesis of mesoporous silica have been proposed in, for example, Chem.Commun., 2147, 1998 and J. Memb. Sci., 182, 235, 2001.

In some fields using a separation membrane enabling a high selectivityand a catalytic support of high performance, for example, the medicinalfield and the food field, alkaline reagents are used. With conventionalseparation membranes and catalytic supports, however, there have beencases that their washing with such an alkaline reagent is impossible orthey have no sufficient durability to the alkaline reagent. Therefore,conventional separation membranes and catalytic supports have not beenfully satisfactory in general applicability. No sufficient solution hasyet been proposed to solve such a problem.

SUMMARY OF THE INVENTION

The present invention aims at providing a mesoporous silica and amesoporous silica composite material, both having superior alkalineresistance and being suitably used particularly as a separation membrane(e.g. a ceramic membrane) or a catalytic support for solid-liquidsystem, in which an alkaline liquid may be used; as well as processesfor producing such a silica and such a composite material.

In order to achieve the above aim, the present invention provides thefollowing mesoporous silica, mesoporous silica composite material andprocesses for producing such a silica and such a composite material.

The mesoporous silica has uniform mesopores and a periodic structure,which contains a Zr element in the form of a Si—O—Zr bond. The Zrcontent in the Si—O—Zr bond, represented by [Zr/(Si+Zr)], is 0.05 to 20mole %.

The mesoporous silica according to the present invention preferably hasa particulate form or a filmy form.

The mesoporous silica according to the present invention includesmesopores having diameters between 1.0 to 3.0 nm and the volume of themesopores is 0.5 to 1.0 cc/g.

The mesoporous silica according to the present invention preferably hasan alkaline resistance index of larger than 10 in terms of pH when analkaline resistance test is conducted and evaluation is made based onthe peak intensity appearing at 2θ=2.5° of X-ray diffraction.

The mesoporous silica according to the present invention can be includedin a composite material having the mesoporous silica deposited on aporous substrate.

A process for producing a mesoporous silica includes mixing a solutioncontaining a surfactant with a solution or dispersion containing a Sisource and a Zr source, and stirring the resulting mixture to form agel. The gel is placed in a pressure vessel and kept at a predeterminedtemperature, and calcined to form particles. The particles are moldedinto a desired shape.

Another process for producing a mesoporous silica composite materialincludes dipping a porous substrate in a solution or dispersioncontaining a Si source and a Zr source. The porous substrate and thesolution or dispersion containing a Si source and a Zr source is placedinto a solution containing a surfactant, and stirred to form a gel. Thegel and the porous substrate are placed in a pressure vessel and kept ata predetermined temperature and then calcined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a), 1(b), 1(c) and 1(d) are graphs each showing the X-raydiffraction pattern of a mesoporous silica before and after an alkalineresistance test.

DETAILED DESCRIPTION OF THE INVENTION

Specific description is made below on embodiments of the mesoporoussilica, mesoporous silica composite material and processes for producingsuch a silica and such a composite material, all according to thepresent invention.

The mesoporous silica of the present invention has uniform mesopores anda periodic structure of an Si—O bond, wherein the Si—O bond contains aZr element in the form of a Si—O—Zr bond and the Zr content in theSi—O—Zr bond, represented by [Zr/(Si +Zr)], is 0.05 to 20 mole %, andpreferably 3 to 5 mole %.

When the Zr content in the Si—O—Zr bond is less than 0.05 mole %, thealkali resistance of the mesoporous silica is insufficient. When the Zrcontent is more than 20 mole %, the degree of the periodic structure ofthe mesoporous silica is low.

The Zr content in the Si—O—Zr bond can be measured by dissolving themesoporous silica in hydrofluoric acid and analyzing the resultingsolution using ICP.

The mesoporous silica of the present invention can take a particulateform or a filmy form.

The mesoporous silica may be deposited on a porous substrate to use as amesoporous silica composite material.

In one process for producing a particulate porous silica, a solutioncontaining a surfactant is mixed and stirred with a solution ordispersion containing a Si source and a Zr source to form a gel. The gelis placed in a pressure vessel and kept at a predetermined temperature.The particles are then calcined and molded into a desired shape.

In one specific process for producing a particulate mesoporous silica, asolution containing a surfactant and a pH-adjusting agent is mixed andstirred with a solution containing a Si source and a Zr source to form agel. The gel is placed in a pressure vessel and kept at a predeterminedtemperature. After a predetermined amount of time, the gel is taken outof the vessel and calcined to remove the surfactant present in the poresformed.

In one process for producing a filmy mesoporous silica (a compositematerial of a porous substrate and a filmy mesoporous silica), a poroussubstrate is dipped in a solution or dispersion containing a Si sourceand a Zr source. The porous substrate and the solution or dispersioncontaining a Si source and a Zr source are added into a solutioncontaining a surfactant and the resulting mixture is stirred to form agel. The gel and the porous substrate are placed in a pressure vesseland kept at a predetermined temperature, and calcining is conducted.

In one specific process for producing a filmy mesoporous silica (acomposite material of a porous substrate and a filmy mesoporous silica),a porous substrate is beforehand dipped in a solution or dispersioncontaining a Si source and a Zr source. The porous substrate and thesolution or dispersion are added into a solution containing a surfactantand a pH-adjusting agent and the resulting mixture is stirred to form agel. The gel and the porous substrate are placed in a pressure vessel,kept at a predetermined temperature and taken out of the vessel andcalcined to obtain a mesoporous silica composite material wherein amesoporous silica film is deposited on a porous substrate. In thisprocess, in order to obtain a filmy mesoporous silica, it is importantthat the porous substrate is beforehand dipped in the solution ordispersion containing a Si source and a Zr source. When the poroussubstrate is not dipped beforehand in the solution or dispersioncontaining a Si source and a Zr source, only particles of mesoporoussilica are formed and no mesoporous silica film is formed on the poroussubstrate.

As the porous substrate used in the present invention, there can bementioned, for example, alumina, cordierite, zirconia, titania andstainless steel.

By the above process, a thin film consisting of a mesoporous silicahaving pore diameters of 1.0 to 2.6 nm can be formed on a poroussubstrate. This thin film is not peeled off when touched by hand.Incidentally, a particulate mesoporous silica and a filmy mesoporoussilica are the same in substance although different in form; therefore,both of them have alkaline resistance.

As the surfactant used in the present invention, there can be mentioned,for example, cetyltrimethylammonium bromide (CTAB),cetyltrimethylphosphonium, octadecyltrimethylphosphonium,benzyltrimethylammonium, cetylpyridinium, myristyltrimethylammonium,decyltrimethylammonium, dodecyltrimethylammonium anddimethyldidodecylammonium and the like.

As the Si source used in the present invention, there can be mentioned,for example, colloidal silica, sodium silicate, silicon alkoxides,tetramethylammonium silicate and tetraethylorthosilicate (TEOS) and thelike.

As the Zr source used in the present invention, there can be mentioned,for example, zirconium-containing compounds such as zirconium alkoxideand the like.

As the pH-adjusting agent used as necessary in the present invention,there can be mentioned, for example, acids such as sulfuric acid,hydrochloric acid and the like; and alkalis such as sodium hydroxide,ammonia and the like. Incidentally, the pH of the reaction system in themesoporous silica production process is preferably adjusted to 1 to 3when an acid agent is used, and to 10 to 13 when an alkaline agent isused.

With respect to the proportions of the individual components used inproducing the mesoporous silica or composite material thereof, of thepresent invention, the proportion of the pH-adjusting agent (sodiumhydroxide) to the Si source, in terms of molar ratio of sodiumhydroxide/Si source, is preferably 0.2 to 0.7, more preferably 0.4 to0.6; and the proportion of the surfactant to the Si source, in terms ofmolar ratio of surfactant/Si source, is preferably 0.03 to 0.8, morepreferably 0.04 to 0.6.

Specifically, when the mesoporous silica produced is MCM-41, the molarratio of sodium hydroxide/Si source is preferably 0.4 to 0.6, and themolar ratio of surfactant/Si source is preferably 0.04 to 0.1. When themesoporous silica produced is MCM-48, the molar ratio of sodiumhydroxide/Si source is preferably 0.4 to 0.6, and the molar ratio ofsurfactant/Si source is preferably 0.4 to 0.6.

In producing the mesoporous silica or the composite material thereof, ofthe present invention, the temperature employed in forming a gel ispreferably room temperature to 30° C. When this temperature is too high,the raw materials for the gel may not reach the inside of the pores ofthe porous substrate.

The formed gel is kept preferably at 20 to 180° C. and, when 90° C. isemployed, the keeping time is preferably 48 hours.

The conditions employed in calcining the gel or the gel and the poroussubstrate are preferably 300 to 500° C. (temperature) and 5 hours(keeping time) when 500° C. is employed.

The present invention is described more specifically below by way ofExamples. However, the present invention is in no way restricted bythese Examples.

EXAMPLES 1 TO 6 Production of Zirconia-Containing MCM-41

50 g of deionized water, 0.364 g of cetyltrimethylammonium bromide(CTAB) as a surfactant and 2.5 g of NaOH (4 mol/l) were placed in abeaker and then stirred at 30° C. for 30 minutes to obtain a solution 1.A mixed solution of tetraethylorthosilicate (TEOS) (a Si source) andtetrapropylzirconium (TPOZ) or tetrabutylzirconium (TBOZ) (a Zr source)was added to solution 1. The resulting mixture was stirred at 30° C. for2 hours to form a gel. The gel was placed in a pressure vessel andallowed to stand at 90° C. for 72 hours. The resulting product was takenout of the pressure vessel and calcined at 500° C. for 4 hours to removethe surfactant (CTAB). XRD diffraction confirmed that the product wasMCM-41. The product was measured for mesopore diameter and mesoporevolume and also subjected to an alkaline resistance test.

Table 1 shows the proportions of TEOS and TPOZ or TBOZ, the Zr contentin zirconia-containing MCM-41, i.e. Zr/(Si+Zr) determined by ICPanalysis, the mesopore diameter and mesopore volume ofzirconia-containing MCM-41, and the result of the alkaline resistancetest of zirconia-containing MCM-41.

EXAMPLES 7 TO 12 Production of Zirconia-Containing MCM-48

In a beaker were placed 44 g of deionized water, 5.83 g of CTAB and 5.0g of NaOH (4 mol/l), followed by stirring at 30° C. for 30 minutes toobtain a solution 2. To this solution 2 was added a mixed solution ofTEOS and tetrapropylzirconium (TPOZ) or tetrabutylzirconium (TBOZ). Theresulting mixture was stirred at 30° C. for 2 hours to form a gel. Thegel was placed in a pressure vessel and allowed to stand for 72 hours.The resulting product was taken out of the pressure vessel and fired at500° C. for 4 hours to remove the surfactant (CTAB) . XRD diffractionconfirmed that the product was MCM-48. The product was measured formesopore diameter and mesopore volume and also subjected to an alkalineresistance test.

Table 1 shows the proportions of TEOS and TPOZ or TBOZ, the Zr contentin zirconia-containing MCM-48, i.e. Zr/(Si+Zr) determined by ICPanalysis, the mesopore diameter and mesopore volume ofzirconia-containing MCM-48, and the result of the alkaline resistancetest of zirconia-containing MCM-48.

COMPARATIVE EXAMPLE 1 Production of MCM-41

In a beaker were placed 50 g of deionized water, 0.364 g of CTAB and 2.5g of NaOH (4 mol/l), followed by stirring at 30° C., to obtain asolution 3. 30 minutes later, 4.17 g of TEOS was added to the solution3, and the resulting mixture was stirred at 30° C. for 2 hours to form agel. The gel was placed in a pressure vessel and allowed to stand at 90°C. for 72 hours. The resulting material was taken out of the pressurevessel and calcined at 500° C. for 4 hours to remove the surfactant(CTAB). XRD diffraction confirmed that the product was MCM-41. Theproduct was measured for mesopore diameter and mesopore volume and alsosubjected to an alkaline resistance test.

Table 2 shows the proportions of the individual components used, themesopore diameter and mesopore volume of MCM-41, and the result ofalkaline resistance test of MCM-41.

COMPARATIVE EXAMPLE 2 Production of MCM-48

In a beaker were placed 44 g of deionized water, 5.83 g of CTAB and 5 gof NaOH (4 mol/l), followed by stirring at 30° C., to obtain a solution4. 30 minutes later, 8.33 g of TEOS was added to the solution 4, and theresulting mixture was stirred for 2 hours to form a gel. The gel wasplaced in a pressure vessel and allowed to stand at 90° C. for 72 hours.The resulting material was taken out of the pressure vessel and calcinedat 500° C. for 4 hours to remove the surfactant (CTAB). XRD diffractionconfirmed that the product was MCM-48. The product was measured formesopore diameter and mesopore volume and also subjected to an alkalineresistance test.

Table 2 shows the proportions of the individual components used, themesopore diameter and mesopore volume of MCM-48, and the result of thealkaline resistance test of MCM-48. TABLE 1 Examples 1 2 3 4 5 6 7 8 910 11 12 Si source TEOS TEOS TEOS TEOS TEOS TEOS TEOS TEOS TEOS TEOSTEOS TEOS 4.04 3.96 3.75 4.04 3.96 3.75 7.92 7.5 7.08 7.92 7.5 7.08 Zrsource TPOZ TPOZ TPOZ TBOZ TBOZ TBOZ TPOZ TPOZ TPOZ TBOZ TBOZ RBOZ 0.260.44 0.89 0.27 0.45 0.90 0.53 0.89 1.78 0.54 0.90 1.81 Zr/(Si + Zr) 0.030.05 0.10 0.03 0.05 0.10 0.03 0.05 0.10 0.03 0.05 0.10 Surfactant CTABCTAB CTAB CTAB CTAB CTAB CTAB CTAB CTAB CTAB CTAB CTAB 0.364 0.364 0.3640.364 0.364 0.364 5.83 5.83 5.83 5.83 5.83 5.83 PH-adjusting NaOH NaOHNaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH NaOH agent 2.5 2.5 2.5 2.52.5 2.5 5.0 5.0 5.0 5.0 5.0 5.0 Product Zr- Zr- Zr- Zr-MCM- Zr-MCM-Zr-MCM- Zr-MCM- Zr-MCM- Zr-MCM- Zr-MCM- Zr-MCM- Zr-MCM- MCM- MCM- MCM-41 41 41 48 48 48 48 48 48 41 41 41 Mesopore 2.6 2.8 diameter Mesopore0.9 1.0 volume Alkaline pH 11.5 pH 11.5 pH 11.5 pH 11.5 pH 11.5 pH 11.5pH 11.5 pH 11.5 pH 11.5 pH 11.5 pH 11.5 pH 11.5 resistance

TABLE 2 Comparative Examples 1 2 Si source TEOS TEOS 4.17 4.17Surfactant CTAB CTAB 0.364 5.83 pH-adjusting agent NaOH NaOH 2.5 5.0Product MCM-41 MCM-48 Mesopore diameter 2.7 2.4 Mesopore volume 0.8 0.9Alkaline resistance Broken at pH 10 Broken at pH 10

The measurements of the mesopore diameter and mesopore volume of eachproduct, the XRD diffraction for identification of each product, and thealkaline resistance test for each product were conducted as follows:

Mesopore diameter: Calculated from the adsorption isotherm of N₂ at 77 Kaccording to the BJH method;

Mesopore volume: Calculated from the amount of adsorbed N₂ at 77 K;

XRD diffraction: Measured in a 2θ range of 15.8 to 8°, using CuK_(α);and

Alkaline resistance test: Solutions of pH 10 to 11.5 each comprisingNaHCO₃ and NaOH were prepared. 0.1 g of a sample was placed in 10 ml ofeach solution, followed by stirring at 30° C. for 3 hours and drying.The resulting material was subjected to XRD diffraction to confirmwhether or not the structure of the sample was maintained.

FIGS. 1(a), 1(b), 1(c) and 1(d) show the X-ray diffraction patterns ofmesoporous silicas before and after the alkaline resistance test. InFIGS. 1(a), 1(b), 1(c) and 1(d), the axis of ordinate refers to a peakintensity and the axis of abscissa refers to 2θ. FIGS. 1(a), 1(b), 1(c)and 1(d) are the X-ray diffraction patterns before and after thealkaline resistance test, obtained in Comparative Example 1, Example 1,Comparative Example 2 and Example 2, respectively. In ComparativeExamples 1 and 2, the structure of mesoporous silica was broken at pH10; in contrast, in Examples 1 and 2, the structure of mesoporous silicawas maintained even at pH 11.5.

As described above, the present invention provides a mesoporous silicaand a mesoporous silica composite material, both having superioralkaline resistance and being suitably used particularly as a separationmembrane (e.g. a ceramic membrane) or a catalytic support forsolid-liquid system, in which an alkaline liquid may be used; as well asprocesses for producing such a silica and such a composite material.

1-12. (canceled)
 13. A process for producing a mesoporous silicacomposite material, which comprises dipping a porous substrate in asolution or dispersion containing a Si source and a Zr source, addingthe porous substrate and the solution or dispersion containing a Sisource and a Zr source, into a solution containing a surfactant,stirring the resulting mixture to form a gel, placing the gel and theporous substrate in a pressure vessel and keeping them at apredetermined temperature, then calcining them.
 14. (canceled)